Treatment strategies for winery wastewater reuse: Performance of ceramic membrane filtration and UV-A LED photo-Fenton oxidation

Addressing climate change and water scarcity in viticultural regions such as Portugal’s Douro Valley requires decentralized, circular strategies for winery wastewater (WWW) treatment and reuse. This study evaluated two winery effluent streams collected during two sample campaigns – after primary decantation (denoted as A RAW ; B RAW ) and collected after aerobic biological treatment (A BIO ; B BIO ) – using tubular ceramic membranes in crossflow filtration – microfiltration (MF), ultrafiltration (UF) and nanofiltration (NF). In addition, UV-A LED photo-Fenton oxidation was assessed as an alternative advanced treatment for the biologically treated effluent to meet the requirements of Portuguese Decree-Law No. 119/2019 for agricultural reuse. Compared with raw effluents, biologically treated wastewater showed 89 – 97% lower organic load (COD, BOD 5 ), 50 – 75% less suspended solids, and 55 – 90% lower total nitrogen. Treating A BIO with a UF 10 nm membrane (6 bar, 20 °C, 4 m s -1 ) achieved 91% BOD 5 removal at a flux of 138 L m -2 h -1 , meeting Class B irrigation standards, although both flux and removal efficiency declined for the higher organic load B BIO stream. Applying the same membrane to A RAW and B RAW – either alone or in a cascade configuration (UF 10 nm → NF 0.9 nm → NF 400 Da) – produced non-compliant permeates (BOD 5 > 450 mg O 2 L -1 ), despite achieving 65% COD and 86% BOD 5 reductions. A continuous UV-A LED photo-Fenton process, optimized via a Box–Behnken design (H 2 O 2 /COD = 0.9, H 2 O 2 /Fe 2+ = 15, τ = 30 min), achieved 54% COD removal in B BIO but limited nutrient reduction, yielding residual BOD 5 values 3 – 4 times above reuse thresholds. Overall, ceramic membranes proved effective as a complementary treatment process for biologically treated effluents up to 550 mg O 2 L -1 . Beyond this limit, neither technology used was independently enough to consistently achieve the water quality standards required for agricultural reuse. • Ultrafiltration at 10 nm met agricultural irrigation norms with 91% BOD₅ removal • Raw WW remained non-compliant despite cascade membrane down to 400 Da cut-off • Residual BOD₅ in permeate limits standalone UF reuse potential • Photo-Fenton enhanced color and COD removals, but failed reuse compliance • Biological treatment step proved essential; membranes act as polishing step